Building Blocks Artist Driven Procedural Buildings. James Golding - Epic Games

Transcription

1 Building Blocks Artist Driven Procedural Buildings James Golding - Epic Games

2 Who Am I Started as Field Engineer at MathEngine Oxford, UK Senior Programmer at Epic Games Raleigh, NC, USA Worked here for nearly 8 years Physics, animation, tools, gameplay Shipped some games Unreal Tournament 2003, 2004, UT3, Gears of War 1 & 2

3 Who Is This Talk For Programmers Level Designers Technical Artists There is no code, I promise! Anyone who thinks about building big cities for games

4 Our Goals Good looking buildings with high visual density Easily change shape and size for gameplay Automatically generate LODs

5 Not Our Goals We are not interested in generating entire city with one button, or even an entire building, but decorating a building defined by designer.

6 Existing Approaches Use level geometry tools, cover with meshes Lots of work placing meshes Painful to change meshing Build custom building meshes Hard to adjust for gameplay Each one needs LOD custom made Simple shapes with tiling material Did not meet our visual bar

7 New Approach Designer creates 'high level' description of building Artists build a library of rectangular, modular, facade meshes Artist creates 'ruleset' which describes how facade pieces are used Initial idea from "Procedural Modeling of Buildings" by Müller et al. (2006, ETH Zurich)

8 Defining Building Shape Collection of simple shapes

9 Defining Building Shape Apply Ruleset to group

10 Defining Building Shape Can easily modify building at any time

11 Breaking It Down Starting with a reference photo

12 Breaking It Down Artist breaks it into modular meshes

13 Breaking It Down Procedural system places meshes

14 Scopes A scope is a 2D rectangle Location Orientation Dimensions Tool takes 3D building shape and extracts set of scopes

15 Extracting Rectangles Certain areas are not rectangular Walls - if roof is not flat Roof - if building plan is non-rectangular We make simple polygons to fill holes Don t extract scope from roof always just big polygon

16 Extracting Rectangles

17 Rules? Each rule can do one of two things: Split a scope into smaller scopes Place mesh that fills the scope area on the building facade Forms a graph

18 Rules? A grammar for describing facades Context Free Graph of nodes good for a graphical tool More visual = happy artists

19 The Rules

20 Mesh Rule Artist specifies What mesh X and Z extent that it fills Easy to scale and place instance scale = desired size/defined size

21 Mesh Rule Initial concerns over scaling of artist built meshes System lets you specify which meshes are scaled and which are not Generally not visually noticeable with buildingtype meshes Needs to avoid tiny doors etc

22 Repeat Rule Choose an axis (X or Z) Break up scope along that axis into equal size pieces Ensure no piece along axis is larger than defined maximum size Generates varying number of new scopes, depending on Generates varying number of new scopes, depending on building size

23 Repeat Rule

24 Split Rule Designer specifies axis and number of scopes to break into. Each split can be fixed size or variable. Always require one of the splits to be variable. If scope is too small to fit in fixed size areas, must discard them. Similar to windowing toolkits (wxsizer etc)

25 Split Rule

26 Alternate Rule Hard to achieve ABABA 'fence post' layout with just repeat and split. A is fixed, B is stretchy.

27 Alternate Rule

28 Occlusion Rule Quickly find that meshes are being placed where not seen Needed for intersections between buildings to look good

29 Occlusion Rule Output is 'clear', 'blocked' or 'partial' Don't place mesh if 'blocked' Can choose different mesh depending on 'clear' and 'partial' Initially this was a separate rule node Used so frequently, we included this into the Mesh rule

30 Occlusion Rule

31 Top/Bottom Rule Don't want shop fronts at the bottom of every scope in building Performs different actions if bottom of scope is at bottom of entire building Does same thing for top (e.g. large trim at very top)

32 Top/Bottom Rule

33 Random Rule Does not resize scope Executes to N out of the M possible child Rules Allows meshes on top of each other E.g. a Window mesh with random AC unit and/or awning.

34 Random Rule Composite regions like random shopfronts

35 Random Rule

36 Random Rule

37 Quad Rule Sometimes you DO want a tiling material Simple variation of Mesh Rule Adjusts UVs to tile base on scope size Same logic as Repeat Rule Second non-tiling UV channel

38 Quad Node

39 Sub Ruleset Allow a Ruleset to refer to other Rulesets Complicated Rulesets can be reused. Terrifying prospect of recursive architecture!

40 Size Rule Simple choice based on dimension Useful for fixing squeezing

41 Size Rule Without Size Rule With Size Rule

42 Variations

43 Variations Each side of a building may need to look different

44 Variations Initially allowed Level Designers to assign rulesets per-face Corners usually looked bad Artists had no control over ruleset Artists had no control over ruleset combinations

45 Variations Each face of a building volume can have a variation name set on it Special rule node uses that to decide which output to fire Level designer can choose front, side etc. Ruleset designer can ensure they all match nicely

46 Variations Context menu on each face offers variations created by artist

47 Variations

48 Corners

49 Trim And Corners Making trim work around corners is one of the hardest parts We came up with three approaches to We came up with three approaches to decorating corners

50 Trim And Corners Build Rulesets with flat edges Only really possible with modern architecture

51 Trim And Corners Cover corner with mesh, at average angle between faces LDs did this manually on previous games

52 Trim And Corners Building custom corner pieces use custom Rule to pick correct piece based on angle lots of custom meshes need making limit LD to certain angles

53 Corner Rule Each scope owns its left edge Use angle to scope on left to pick mesh Asks scope to right how much space to leave there

54 Corner Rule Allows mixing rule sets with different corner sizes

55 Corner Rule This requires edge<->scope map Array of top level scopes Array of edges I am scope 3 s left edge and scope 12 s right edge This is my start and end location This is my angle Build this map as part of scope extraction

56 Corner Rule Requires each edge to only have 2 scopes

57 Corner Rule Split entire building at each roof level

58 Corner Rule Also produces pleasing architecture

59 Corner Rule

60 Other Features

61 Curved Corners Roof From each vertex of roof poly, can find its Corner Rule Add options to Corner Rule to describe corner shape Use that to reshape the corner

62 Roof

63 Floor Option to run rules on top of big floor poly

64 Player Collision Can use the simple 'building volume Fast Smooth Certain meshes can be flagged as having collision in addition to this

65 Parameters Expose parameters in shaders applied to building pieces Wall Diffuse and Specular Color Window Diffuse and Specular Color Gives more variation for no memory cost

66 Rendering Approach Buildings tend to be made of many copies of a few meshes trim, window frame, columns Lots of draw calls Initially tried merging meshes to reduce sections Huge vertex/index buffers!

67 Rendering Approach Instanced rendering! Different on all 3 platforms Need to duplicate index buffer etc. Trade-off index buffer memory for speed

68 Window Interiors

69 Window Interiors Three textures - one for each depth

70 Window Interiors Use mask to offset texture UV based on cam vector

71 Window Interiors Pack all masks into one texture

72 LOD

73 Building LOD Low LOD mesh is automatically created Mesh the same shape as the volume used to construct building Renders high detail meshes into texture All faces atlassed into one texture Low LOD mesh is always loaded Textures can stream in different mip levels

74 Building LOD

75 Windows Buildings all have glass windows reflective with cubemaps LOD needs a mask for reflective windows losing reflection creates very noticeable pop

76 Windows We render 3 passes: Diffuse Window Mask Lighting

77 Windows Diffuse + Window Mask Mask stored as 1 bit alpha in DXT1 Lighting Lower resolution

78 Windows Advantages to 2 texture approach: Lighting texture can be lower resolution Lets us light cubemap glass areas Allows building instances Share Diffuse but unique Lighting Reduces variety of buildings, but uses less LOD texture memory

79 Building LOD

80 Transitions Using dither approach to transition Objects attached to building change when building does A/C units, pipes, signs etc Captured by render-to-texture process

81 Transitions

82 Transitions

83 LOD Quad Idea for automatic intermediate LOD All meshes after rule collapse to single quad Quad uses LOD texture

84 LOD Quad

85 What s Next

86 What s Next More orthogonal variation channels Decal support within ruleset Apply rules to triangular regions Interiors Transition (doors) Collision

87 Conclusion

88 Conclusion Good looking buildings with high visual density Easily change shape and size for gameplay Automatically generate LODs

89 Conclusion Keeps artist and level designer workflows from colliding One change to a ruleset, the whole city changes Artists willing to learn a crazy new system and push it are invaluable and awesome Thanks Pete

90 Conclusion Rulesets everywhere!

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